1. Field of the Invention
The present invention relates to a spin valve element and a thin film magnetic head, and particularly to a spin valve element and a thin film magnetic head having both high sensitivity to an external magnetic field and a high rate of change in magnetoresistance.
2. Description of the Related Art
Magnetoresistive magnetic heads include a MR (Magnetoresistive) head comprising an element exhibiting a magnetoresistive effect, and a GMR (Giant Magnetoresistive) head comprising an element exhibiting a giant magnetoresistive effect. In the MR head, the element exhibiting a magnetoresistive effect has a single layer structure comprising a magnetic material. On the other hand, in the GMR head, the element exhibiting a magnetoresistive effect has a multilayer structure in which a plurality of materials are laminated. Although there are several types of structures creating the giant magnetoresistive effect, a spin valve element has a relatively simple structure and exhibits a high rate of change in resistance with an external magnetic field.
Recently, high-density magnetic recording has been increasingly demanded, and a spin valve element adaptable for higher recording density has increasingly attracted attention.
A conventional spin valve element is described with reference to the drawings. FIG. 31 is a schematic sectional view showing a conventional spin valve element 301 as viewed from the magnetic recording medium side.
Furthermore, shield layers are formed above and below the spin valve element 301 with gap layers provided therebetween to form a reproducing thin film magnetic head comprising the spin valve element 301, the gap layers and the shield layers. A recording inductive head may be laminated on the thin film magnetic head.
The thin film magnetic head is provided at the trailing side end of a floating slider together with the inductive head to constitute a thin film magnetic head which detects a recording magnetic field of a magnetic recording medium such as a hard disk or the like.
In FIG. 31, the Z direction coincides with the movement direction of the magnetic recording medium, the Y direction coincides with the direction of a leakage magnetic field from the magnetic recording medium, and the X1 direction coincide with the track width direction of the spin valve element 301.
The spin valve element 301 shown in FIG. 31 is a bottom-type single spin valve thin film magnetic element comprising an antiferromagnetic layer 303, a pinned magnetic layer 304, a nonmagnetic conductive layer 305, and a free magnetic layer 311, which are laminated in turn.
In FIG. 31, reference numeral 300 denotes an insulating layer made of Al2O3 or the like, and reference numeral 302 denotes an underlying layer made of Ta (tantalum) or the like and laminated on the insulating layer 300. The antiferromagnetic layer 303, the pinned magnetic layer 304, the nonmagnetic conductive layer 305 made of Cu or the like, and the free magnetic layer 311 are laminated on the underlying layer 302, and a capping layer 320 made of Ta or the like is laminated on the free magnetic layer 311.
In this way, the layers from the underlying layer 302 to the capping layer 320 are laminated in turn to constitute a laminate 321 having a substantially trapezoidal sectional shape having a width corresponding to the track width.
The pinned magnetic layer 304 is made of, for example, Co, and laminated in contact with the antiferromagnetic layer 303 so that an exchange coupling magnetic field (exchange anisotropic magnetic field) occurs in the interface between the pinned magnetic layer 304 and the antiferromagnetic layer 303 to pin the magnetization direction of the pinned magnetic layer 304 in the Y direction shown in the drawing.
The free magnetic layer 311 comprises a nonmagnetic intermediate layer 309, and first and second free magnetic layers 310 and 308 formed with the nonmagnetic intermediate layer 309 provided therebetween. The first free magnetic layer 310 is provided on the capping layer 320 side of the nonmagnetic intermediate layer 309, and the second free magnetic layer 308 is provided on the nonmagnetic conductive layer 305 side of the nonmagnetic intermediate layer 309. The thickness of the first free magnetic layer 310 is slightly larger than the thickness of the second free magnetic layer 308. The first and second free magnetic layers 310 and 308 are antiferromagnetically coupled with each other so that both layers are put into a ferrimagnetic state.
The first free magnetic layer 310 comprises a ferromagnetic conductive film made of a NiFe alloy or the like, and the nonmagnetic intermediate layer 309 is made of a nonmagnetic material such as Ru or the like.
The second free magnetic layer 308 comprises a anti-diffusion layer 306 and a ferromagnetic layer 307. Each of the anti-diffusion layer 306 and the ferromagnetic layer 307 comprises a ferromagnetic conductive film, and for example, the anti-diffusion layer 306 is made of Co, and the ferromagnetic layer 307 is made of a NiFe alloy.
The anti-diffusion layer 306 is provided for preventing mutual diffusion between the ferromagnetic layer 307 and the nonmagnetic conductive layer 305 to increase the GMR effect (ΔMR) produced in the interface with the nonmagnetic conductive layer 305.
Since the first free magnetic layer 310 and the second free magnetic layer 308 are antiferromagnetically coupled with each other, when the magnetization direction of the first free magnetic layer 310 is oriented in the X1 direction shown in the drawing by bias layers 332, the magnetization direction of the second free magnetic layer 308 is oriented in the direction opposite to the X1 direction. At this time, the magnetization of the first free magnetic layer 310 remains to orient the magnetization direction of the entire free magnetic layer 311 in the X1 direction shown in the drawing.
In this way, the first free magnetic layer 310 and the second free magnetic layer 308 are antiferromagnetically coupled with each other so that the magnetization directions are antiparallel to each other to bring the free magnetic layer 311 into a synthetic ferrimagnetic state (synthetic ferrimagnetic free).
Therefore, the magnetization direction of the free magnetic layer 311 crosses the magnetization direction of the pinned magnetic layer 304.
The bias layers 332 are formed on both sides of the laminate 321. The bias layers 332 orient the magnetization direction of the first free magnetic layer 310 in the X1 direction to bring the free magnetic layer 311 in a single magnetic domain state, suppressing Barkhousen noise of the free magnetic layer 311.
Reference numeral 334 denotes a conductive layer made of Cu or the like, for applying a sensing current to the laminate 321.
Furthermore, bias underlying layers 331 made of, for example, Cr or the like are provided between the bias layers 332 and the insulating layer 300, and between the bias layer 332 and the laminate 321, and intermediate layers 333 made of, for example, Ta or Cr are provided between the bias layers 332 and the conductive layers 334.
In the spin valve thin film magnetic element 301, when the magnetization direction of the free magnetic layer 311, which is oriented in the X1 direction, is changed by a leakage magnetic field from the recording medium such as a hard disk or the like, the electric resistance changes with the relation to magnetization of the pinned magnetic layer 304 which is pinned in the Y direction, and the leakage magnetic field from the recording medium is detected by a voltage change based on the change in the electric resistance.
The free magnetic layer 311 comprises the first and second free magnetic layers 310 and 308 antiferromagnetically coupled with each other, and the magnetization direction of the entire free magnetic layer 311 changes with an external magnetic field of small magnitude, thereby increasing the sensitivity of the spin valve thin film magnetic element 301.
Particularly, the thicknesses of the first and second free magnetic layers 310 and 308 can be appropriately controlled to decrease the effective thickness of the free magnetic layer 311 so that the magnetization direction of the free magnetic layer is easily changed with an external magnetic field of small magnitude to increase the sensitivity of the spin valve element 301.
The conventional spin valve element 301 comprises the free magnetic layer 311 having a laminated structure of three layers including the first and second free magnetic layers 310 and 308, and the nonmagnetic intermediate layer 309. Therefore, the thickness of the laminate 321 is increased to cause a shunt of the sensing current. This causes the problem of decreasing conduction electrons flowing through the nonmagnetic conductive layer 305 to cause a so-called shunt loss in which the rate of change in magnetoresistance of the spin valve element 301 is decreased.
In order to decrease the shunt loss of the spin valve element, it is effective that the free magnetic layer has a single layer structure to decrease the thickness of the laminate. In this case, there is the problem of slowing down a change in the magnetization direction of the free magnetic layer in response to an external magnetic field, thereby decreasing the sensitivity to the external magnetic field.